The purpose of this study is to describe and evaluate the natural history of the Human T-Lymphotropic Virus I (HTLVI) in a highly endemic population in southwestern Japan. HTLVI is a latent retrovirus which is known to produce adult T-cell leukemia/lymphoma in about 1% of all infected and is associated with spastic paraparesis or HAM). The study population consists of about 1500 persons or approximately 63% of all adults residing in two coastal villages in southeastern Miyazaki Prefecture. Of these, approximately 1 in 3 have HTLVI antibodies are presumed carriers. The population will be prospectively followed for five years with clinical, serologic, and interview information collected annually. The study will focus on four areas: 1. The prospective follow-up of subjects for the presence, level, and progression or regression of "atypical' lymphocytes (virus- infected, TAC-positive T-cells). The presence and clonality of HTLVI provirus will be evaluated by southern blotting technique on all subjects with any detectable level of circulating atypical lymphoctyes, and a sample of those without. 2. The prospective follow-up of subjects for the presence, level and progression or regression of a diminished level of response to PPD skin testing, indicative of subclinical immunosuppression. 3. Clarification of the risk of infection by sexual exposure by evaluation of a variety of measures of virus status among married couples who are discordant for carrier status, in comparison to similarly aged couples who are both infected, and to those where seroconversion is observed. 4. Surveillance of the seronegative population for seroconversion and continued evaluation of the clustering of infection within families. With information on familial relationships available for almost the entire cohort, we will attempt to identify all persons who are "indirectly" (non-sexual, non-perinatal) exposed to a carrier within households as a means of addressing the risk of such exposure. HTLVI antibody assays include detection of IgM, anti- gag proteins, and titration of anti p42, the trans-activating protein. The population will continue to be followed for opportunistic infections, and HAM,and the identification of additional intermediate markers of progression toward ATL will be sought.